A typical thin film magnetic recording head or transducer is configured with two magnetic thin film layers that are formed of a nickel-iron composition, such as Permalloy material, and which are generally designated as the P1 and P2 layers. The P1 and P2 layers sandwich an electrical coil surrounded by insulating material. The P1 and P2 layers form a back closure whereas the pole tip region adjacent to the transducing gap is narrowed to approximate a relatively smaller funnel-like portion. The Permalloy material is characterized by a magnetic domain structure, which in its ideal form should consist of vertical hexagonal domains, with their easy axes perpendicular to the direction of flux propagation, on every section of the head. However, it has been observed that most magnetic heads show horizontal domains, with the undesirable easy axes parallel to the direction of flux flow, on the P2 pole-tip region of the head. These horizontal domains do not return to their equilibrium configurations after an external magnetic field is applied. Signal noise also known as "wiggles" is generally caused by the instability of magnetic domain walls.
Major causes of the undesirable easy axes formation are the compressive stress which occurs at the narrowed pole tip region, and the variations of the Permalloy compositions, or the nickel to iron ratios. It is very difficult, from a manufacturing standpoint, to strictly control these two factors. Composition uniformity to specifications is costly and difficult to control, due to the complicated head geometries and the large stack height variation across the head. Stress control is extremely difficult to achieve, since a complete head consists of more than ten layers and has to go through several annealing processes. The stresses of each layer change not only after each layer is stacked, but also after the Permalloy experiences each annealing process. Although stresses of each single layer can be carefully controlled during fabrication, they still become unpredictable after a complete head is made. Therefore, strict composition and stress control are difficult to produce heads reliably with the desirable easy axes near the pole tip region.
FIG. 1 illustrates a prior art transducer designated by reference numeral 2. The hatched area 3 represents the portions of the two poles P1 and P2 in direct contact at the back closure region. The ideal magnetic domain pattern 4 of the magnetic pole is illustrated with dashed lines. The ideal domain pattern 4 generally comprises a plurality of main domains 6 surrounded by a plurality of closure domains 8. The magnetic domains 6 and 8 are partitioned in an orderly manner by domain walls 10. The direction of magnetization in each of the magnetic domains 6 and 8 are oriented in parallel with their respective groups of easy axes 6A-6B and 8A-8B. Domain pattern 4 is an ideal design goal in which the easy axes of the main domains 6A and 6B are perpendicular to the directions of flux flow 12 and 14 during the write and read modes, respectively. However, in practice, securing an ideal magnetic domain pattern 4 in the magnetic poles as shown in FIG. 1 is not easy. The formation of an equilibrium magnetic domain pattern in the magnetic poles depends on a variety of factors. Examples of the various factors are the geometrical shape, thickness, granular defects, temperature and mechanical stress and composition of the magnetic poles. The underlying principle is that the final domain pattern always stabilizes itself to achieve the lowest magnetic energy state. However, the final domain pattern is unpredictable. This is especially true when the magnetic poles are fabricated through a large number of manufacturing steps. To compound the situation further, the magnetic domain pattern is ever changing under the influence of external factors. A change in the magnetic domain pattern during normal operation manifests itself as electrical noise which is detrimental to the performance of the magnetic transducer.
To illustrate the dynamic nature of the magnetic domains in the magnetic pole, assume that the ideal magnetic domain pattern 4 as shown in FIG. 1 is established in the magnetic pole after manufacturing. The undesirable domain configuration, such as pattern 5 shown in FIG. 2, occurs frequently. Typically, some of the domain walls merge together resulting in a reduced number of main and closure domains 6 and 8. This time, the easy axes of some of the domains, such as axes 18A and 18B of domains 18, may not be perpendicular to the flux direction 12. Domains 18 are sometimes called horizontal domains, in contrast with the vertical domains 20 in which the easy axes 20A and 20B are perpendicular to the direction of magnetic flux 12. Upon the withdrawal of the write current, the domain configurations in FIG. 2 do not return to their original equilibrium positions after each write action. Therefore the readback signal changes after each write action. The readback signal also shows the undesirable signals superimposing on the major peak, which can cause bit shift that results in higher error rate. These noises are commonly called "wiggles". A transducer thus fabricated is not suitable for high frequency and high recording density applications.
Various techniques have been suggested and attempted in the past for securing stable domain patterns in the magnetic poles. For example, alloy composition in the magnetic poles has been plated with high degree of uniformity under tight monitoring controls, in an effort to prevent domain formations along the sites of alloy granular defects. Magnetic poles have also been designed with geometrical shapes having proper aspect ratios to accommodate the natural periodicity of the magnetic domains. None of these techniques has demonstrated any satisfactory working results.
The constant demand for electronic products with compact sizes and portable features prompts manufacturers to provide storage devices with ever decreasing geometries. As a result, recording media are designed for narrower track widths and higher linear recording density applications. Transducers with high error rate are incapable of interacting with such recording media. There is a long-felt and increasing need for a magnetic transducer free of the aforementioned problems.